Jet deflection vapor gage

ABSTRACT

A gage for measuring the flow rate of a vapor in an evacuated chamber has a narrow jet of air directed across an opening through which a stream of the vapor passes. The vapor deflects the air jet in proportion to the amount of material in the vapor stream. The flow rate is determined by measuring the air pressure on the side of the opening opposite the air jet.

United States Patent Rudolph [451 June 20, 1972 [54] JET DEFLECTIONVAPOR GAGE [72] Inventor: Ralph G. Rudolph, Edgewood Borough,

[73] Assignee: United States Steel Corporation [22] Filed: Dec. 5, 196921 Appl. No.: 882,540

FOREIGN PATENTS OR APPLICATIONS l ,5 18,845 3/ 1968 France ..73/194Schmaeng ..73/194 Primary Examiner-Richard C. Queisser AssistantExaminer-C. E. Snee, lll Attomey-Rea C. Helm [57] ABSTRACT A gage formeasuring the flow rate of a vapor in an evacuated chamber has a narrowjet of air directed across an opening through which a stream of thevapor passes. The vapor deflects the air jet in proportion to the amountof material in the vapor stream. The flow rate is detennined bymeasuring the air pressure on the side of the opening opposite the airjet.

5 Claims, 6 Drawing Figures PHENTEDJUNZO m2 SHEET 10F 2 A 5&3, fit niwQ2383 twig m m (6 (6 M N v \Q m r. ti 4 71 wmw J I II ll 1 4 NN fiLl|nilll llr (m v v FIIIL M Attorney JET DEFLECTION VAPOR GAGE Thisinvention relates to a gage for measuring vapor flow and moreparticularly to a gage for measuring the evaporan'on or flow rate of amaterial heated in an evacuated chamber to vaporizing temperature.

In certain processes, such as the deposition of aluminum vaporized by anelectron beam gun on a steel strip, it is necessary to measure theevaporation rate of a material heated to vaporizing temperature in anevacuated chamber to determine evaporation efficiency, coating rate,vapor distribution, and system malfunctions to preclude manufacture ofinferior product and excessive line down time.

Such a gage must be able to operate in a high vacuum, in changingpressure levels, in temperatures up to 400 F and in fluctuating electricand magnetic fields of strong intensity. The gage must measureelectrically ionized vapor particles at high evaporation rates forsustained periods of time in the presence of free electrons.

Measuring devices with which I am familiar all fail to meet one or moreof these requirements. Quartz crystal gages, in which changes inresonant frequency is measured as vapor condensation builds up on thecrystal surface, are limited to the time required to accumulate ameasurable deposit and are not suitable for high evaporation rates.Ionization gages which measure the charge on insulated plates when anelectron beam ionizes a portion of the vapor it passes through aresuitable for low evaporation rates, are sensitive, require shielding andmust be cleaned after about 3 hours use. X-ray gages which measure theamount of characteristic radiation the vapor emits when X-rays passthrough it are complex, difficult to shield, respond slowly and must becleaned frequently. X-ray or beta-ray thickness gages which measure thethickness of coating deposited on a substrate exposed to the vaporrespond too slowly and are inaccurate since the thickness of coating isnot a function of the evaporation rate alone.

According to my invention, I pass a narrow jet of gas through a vaporstream perpendicular to the direction of flow and measure the resultantgas pressure on the other side of the vapor stream with a Pirani gage.This pressure is proportional to the amount of metal passing through thestream or the evaporation rate. This provides a fast, stable andsensitive measure of high level evaporation rates.

It is, therefore, an object of my invention to provide a sensitivestable apparatus for measuring high intensity metal evaporation ratewith a fast response.

Another object is to provide such an apparatus that can operate inchanging pressures, a high vacuum, high temperatures and in strongfluctuating magnetic and electric fields.

These and other objects will become more apparent after referring to thefollowing drawings and specification, in which:

FIG. 1 is a plan view of a deposition chamber showing the gage blocklocation;

FIG. 2 is a sectional elevation of the deposition chamber of FIG. 1along line lI-ll;

FIG. 3 is a block diagram of the control circuit of the gage;

FIG. 4 is a plan view showing details of the gage block;

FIG. 5 is an elevation of the block showing details and connections tothe block; and

FIG. 6 is a sectional view of the block along line Vl-Vl.

Referring now to the drawings, reference numeral 2 indicates a vacuumdeposition chamber. Strip S passes through chamber 2 between sealingrolls 4 to be coated by a deposit of aluminum vapor. A crucible 6resting on bottom 8 of chamber 2 contains aluminum 10 which is vaporizedto a vapor V by an electron beam gun (not shown). This is a conventionalaluminum coating apparatus.

A brass gage block 12 is disposed inside chamber 2 so that part of thevapor V from crucible 6 passes through a generally rectangularcross-sectional shaped aperture 14 in gage block 12. A needle jet 16,such as a number 25 gage hypodermic needle projects at right angles froma centrally disposed location in one face of aperture 14 which isparallel to the direction of flow of vapor V. A source of gas such asair 18, which is at a pressure higher than that inside chamber 2, is

connected to jet 16 by a conduit 20, which may be one-fourth -inchcopper tubing, through a needle valve 22. A cooling jacket 24 surroundsconduit 20. Cooling passages 26 are located in the sides of block 12 andare connected to jacket 24 and a conventional pump and reservoir system28 to circulate cooling water 30. Side faces 32 of aperture 14 areparallel to the direction of vapor flow and extend from the vapor entryend of aperture 14 to'the level of needle jet 16. The face of aperture14 opposite jet 16 is parallel to the direction of flow from the vaporentry end to the level of needle jet 16 where face 34 slopes away fromjet 16 at an angle of about 30 to the exit end of aperture 14.

Centered in block 12 on the face of aperture 14 opposite jet 16 is anopening 36 having a counterbore 38 at the end remote from aperture 14. Athermal-conductivity tube 40, such as a Pirani gage tube, Type 220l03-l5manufactured by Consolidated Electrodynamics Corporation, Rochester, NewYork, will all but I inch of the metal shell at the base removed, isfitted in block 12 so that open tube element 42 and closed tube element44 are centered in opening and the remaining metal shell fitscounterbore 38. Conduit 26 is shown as discontinued from 260 to 26b inFIG. 5 to better illustrate the location of tube 40. Open element 42 isin axial alignment with jet 16. A base 46 of tube 40 has connections 48to a bridge 50in a control circuit 52 located outside of chamber 2.

In control circuit 52, a 110 volt, 6O cycle power supply 54 drives aconventional oscillator'56 to provide a 25 kilocycle output which isamplified by amplifier 58 and is connected to bridge circuit 50. Bridgecircuit 50 is connected to tube elements 42 and 44 and a potentiometer60. The output of bridge circuit 50 is connected to an amplifier 62which is connected to a non-linear type rectifier 64 having outputterminals 66 and an output ammeter 68.

To operate my gage, control circuit 52 is energized, the air flow rateis set by needle valve 22 and the cooling water turned on. Potentiometer60 is adjusted to zero. Gage block 12 is aligned so that vapor V fromcrucible 6 will pass through aperture 14 perpendicular to the flow ofair from jet 16.

As metallic vapor passes through aperture 14, the amount of air arrivingat element 42 decreases as the air stream from jet l6 interacts with anincreasing vapor stream. This decreases the pressure on element 42,increases the element resistance and unbalances the bridge circuit 50sending a signal to amplifier 62 which is proportional to the rate offlow of vapor passing through aperture 14. With the flow rate throughaperture 7 14 known, the evaporation rate is then determined from theknown proportion of the total vapor that passes through aperture 14.Since the element 42 has a non linear response, the signal fromamplifier 62 is then rectified in rectifier 64 to provide a directcurrent signal on meter 68 and a linear direct current signal forprocess control purposes at tem'rinals 66.

The Pirani gage may operate on direct current but alternating current of10 kilocycles to 25 kilocycles is preferred to minimize noise created bythe electron beam and the gas jet. Direct current would not be desirablein the surroundings of free electrons and ionized gas.

Although the gage operates in an evacuated chamber, the amount of aircoming out of the jet is so small that it does not affect the depositionof metallic vapor in chamber 2. The sloping face 34 is provided so thatair may move in the direction of the vapor stream away from the entry toelement 42 and thus continuously provide a reading on meter 68. Thecooling jacket 24 maintains the air at a constant temperature as itemerges from jet 1 6 to minimize the variation in gage readings causedby gas temperature changes. Air is used because it is readily available,other gases are also satisfactory. Cooling block 12 by circulatingcooling water 30 through passages 26 eliminates any variation caused bytemperature differences between element 42 and element 44 of tube 40 andalso While my gage has been described for measuring aluminum vapor in anevacuated chamber, it may be used to measure the evaporation or flowrate of any material heated to vaporinng temperature in an evacuatedchamber provided a stream may be directed through aperture 14perpendicular to jet 16.

While one embodiment of my invention has been described, it is obviousthat other modifications may be made.

I claim:

1. Apparatus for measuring the flow rate of a vapor stream locatedinside an evacuated chamber comprising a gage block located inside thechamber and having an aperture in axial alignment with the direction offlow of the vapor stream and through which a part of the vapor streamflows, means for directing a narrow stream of gasfrom one side of theaperture across the aperture generally perpendicular to the direction offlow of the vapor stream so that the gas stream will be partiallydeflected by the vapor stream, a thermal-conductivity gage on the sideof the aperture opposite the means for directing the gas, said gagehaving an open unit in axial alignment with the gas stream and a closedunit, a source of high frequency power, a bridge circuit connected tothe power source having one arm connected to the closed unit and anotherarm connected to the open unit, and means connected to the bridgecircuit output for indicating gas pressure on the open unit.

2. Apparatus according to claim 1 in which the means for directing astream of gas includes a needle jet located in the gage block, a sourceof gas under pressure greater than the pressure in said chamber, a gasconduit connecting the needle jet to the gas source, a liquid coolingmedium, a cooling jacket surrounding the gas conduit, a cooling passagein said block connected to said jacket, and a recirculating coolingliquid system connected to the jacket and the passage for circulatingthe cooling medium.

3. Apparatus according to claim 1 in which the aperture has four facesand a generally rectangular cross-sectional shape, the means fordirecting a stream of gas terminates on a centrally disposed location onone face which is generally parallel to the direction of vapor flow, theface opposite the gas directing means is parallel to the direction ofvapor flow from the vapor entry end to the measuring means and slopesprogressively further away from the gas directing means from themeasuring means to the vapor exit end, and the third and fourth facesare generally'parallel to the direction of vapor flow and extend fromthe vapor entry end to an intersection with a plane perpendicular to thedirection of vapor flow and containing the gas stream, therebyfacilitating the flow of gas away from the measuring means.

4. Apparatus according to claim 3 in which the means for directing astream of gas includes a needle jet located on said one face of theaperture, a source of gas under pressure greater than the pressure insaid chamber, a gas conduit connecting the needle jet to the gas source,a liquid cooling medium, a cooling jacket surrounding the gas conduit, acooling passage in said block connected to said jacket, and arecirculating cooling liquid system connected to the jacket and thepassage for circulating the cooling medium.

5. Apparatus according to claim 4 which includes an electron beam gun inthe evacuated chamber, and in which the gas is air, and the vapor isaluminum heated to vaporization by the electron beam gun.

18 I I l

1. Apparatus for measuring the flow rate of a vapor stream locatedinside an evacuated chamber comprising a gage block located inside thechamber and having an aperture in axial alignment with the direction offlow of the vapor stream and through which a part of the vapor streamflows, means for directing a narrow stream of gas from one side of theaperture across the aperture generally perpendicular to the direction offlow of the vapor stream so that the gas stream will be partiallydeflected by the vapor stream, a thermal-conductivity gage on the sideof the aperture opposite the means for directing the gas, said gagehaving an open unit in axial alignment with the gas stream and a closedunit, a source of high frequency power, a bridge circuit connected tothe power source having one arm connected to the closed unit and anotherarm connected to the open unit, and means connected to the bridgecircuit output for indicating gas pressure on the open unit. 2.Apparatus according to claim 1 in which the means for directing a streamof gas includes a needle jet located in the gage block, a source of gasunder pressure greater than the pressure in said chamber, a gas conduitconnecting the needle jet to the gas source, a liquid cooling medium, acooling jacket surrounding the gas conduit, a cooling passage in saidblock connected to said jacket, and a recirculating cooling liquidsystem connected to the jacket and the passage for circulating thecooling medium.
 3. Apparatus according to claim 1 in which the aperturehas four faces and a generally rectangular cross-sectional shape, themeans for directing a stream of gas terminates on a centrally disposedlocation on one face which is generally parallel to the direction ofvapor flow, the face opposite the gas directing means is parallel to thedirection of vapor flow from the vapor entry end to the measuring meansand slopes progressively further away from the gas directing means fromthe measuring means to the vapor exit end, and the third and fourthfaces are generally parallel to the direction of vapor flow and extendfrom The vapor entry end to an intersection with a plane perpendicularto the direction of vapor flow and containing the gas stream, therebyfacilitating the flow of gas away from the measuring means.
 4. Apparatusaccording to claim 3 in which the means for directing a stream of gasincludes a needle jet located on said one face of the aperture, a sourceof gas under pressure greater than the pressure in said chamber, a gasconduit connecting the needle jet to the gas source, a liquid coolingmedium, a cooling jacket surrounding the gas conduit, a cooling passagein said block connected to said jacket, and a recirculating coolingliquid system connected to the jacket and the passage for circulatingthe cooling medium.
 5. Apparatus according to claim 4 which includes anelectron beam gun in the evacuated chamber, and in which the gas is air,and the vapor is aluminum heated to vaporization by the electron beamgun.